A field effect transistor (FET) operates by applying a potential to the gate of the transistor, which changes the density of charge carriers in the channel of the transistor. The threshold potential of the transistor may be understood as the gate potential at which the transistor changes from the off state, in which minimal current flows through the channel, to the on state, in which a pre-defined current flows through the channel. Reliable operation of the transistor depends on the threshold potential remaining constant during the operational lifetime of the transistor. Charges tend to accumulate between the gate and the channel, in the gate dielectric layer, and thus adversely affect the reliability by shifting the threshold potential. Charge accumulation is particularly problematic in gate dielectric layers which include silicon nitride.